Carbocationic polymerizations are well known and provide many polymers such as isobutylene polymers and copolymers (butyl rubber). They are also known for their ability to form block copolymers and telechelic polymers. They are typically conducted in chlorinated hydrocarbon solvents at temperatures between -20 and -1000.degree. C. The chlorinated hydrocarbon solvents are used because they have sufficient polarity to stabilize the transition states, and thus lower the activation energy for ion generation in carbocationic polymerization. The low temperatures are used to slow the termination and chain transfer processes that limit the growth in the molecular weight of the polymer chains. Less polar solvents are less effective at stabilizing transition states, and thus fewer carbocations are produced that are active in polymerization. The solvent also needs to act as a fluid heat transfer medium to dissipate the heat of polymerization. The solvent should dissolve the ingredients of the polymerization.
Carbocationic polymerizations are described by J.P. Kennedy and E. Marechal in "Carbocationic Polymerization" published by Wiley-Interscience, New York, 1982. Carbocationic polymerizations are chain polymerizations where an active species (thought to be carbocations) is created from one or more terminal carbon atoms of a molecule (i.e., one molecule may have two or more carbocation termini). These active terminal carbons are capable of reacting with unsaturated carbons of olefinic type monomers forming a carbon-carbon single bond between the active terminal carbon and one of the unsaturated carbons in the olefin. In the course of this addition reaction, an active species is generated from a carbon in the olefin type monomer. Since an active cationic terminus is regenerated after each reaction of a terminal cation, the process can proceed to high molecular weight materials from unsaturated olefinic monomers.
Carbocationic polymerizations are distinguished from free radical and anionic polymerizations even though all three are chain polymerizations. Carbocationic polymerizations are thought to occur by adding monomers to a terminal carbocation. Radical polymerizations occur by adding monomers to a terminal free radical. Anionic polymerizations are characterized by adding monomers to a negatively charged terminal carbon. One skilled in polymerizations distinguishes these three polymerization types by the ability (or inability) to add olefinic monomers or copolymerize with certain monomers. These types of polymerizations may also be distinguished by their sensitivity to termination by various species known to terminate anions, cations, or free radicals. These matters are explained in George Odian's book "Principles of Polymerization" Wiley Interscience: New York, 2nd ed, pp 180-183, 340-341.
Attempts were made to carbocatienically polymerize isobutylene using coinitiators 2-chloro-2,4,4-trimethylpentane/TiCl.sub.4 at -50.degree. C. in liquid carbon dioxide (CO.sub.2) but this resulted in heterogeneous (precipitation) polymerizations and ill-reproducible results. R.H. Biddulph and P.H. Plesch, The Low-Temperature Polymerization of Isobutene. Part IV Exploratory Experiments., J. Chem. Soc., 1966, 3913 (1960), discussed polymerizations of isobutylene in liquid CO.sub.2 using TiCl.sub.4 or AlBr.sub.3.
Estimates were made of the highest probable molecular weight of a polyisobutylene obtainable at 41.degree. C. in traditional chlorinated solvents by carbocationic techniques instead of at -100.degree.. Based on the increase in the rates of chain termination and chain transfer at the higher temperature, it is anticipated based on extrapolation of the data in J. P. Kennedy Cationic Polymerization: A critical Inventory,"John Wiley Interscience, New York, 1975, that the molecular weight of the polymer produced would decrease from 1,000,000 at -100.degree. C. to about 400 at polymerization temperatures of 36.degree. C.
Supercritical carbon dioxide (SC.multidot.CO.sub.2) has been used for a variety of applications (e.g., to decaffeinate coffee, to liquify coal, to remove cholesterol from egg yolks) and a considerable body of knowledge exists on its use in extractions. Carbon dioxide is supercritical at and above 31.1.degree. C. and at or above 73 atmospheres.